As semiconductor devices become more highly-integrated and operate at higher speeds, metal interconnections formed in the semiconductor device may become micro-sized and multi-layered.
Such metal interconnections may be formed by exposing and developing a photoresist film to make a photoresist film pattern, and then etching the metal layer, for example using photoresist film pattern as a mask. In addition, to reduce a signal delay caused by low resistance and capacitance of the metal interconnection, copper may be used.
Copper may rarely be etched as compared with other metals. Thus, to make a copper interconnection, a damascene process may be performed. In a damascene process, a trench may be formed and a copper layer may be formed to fill the trench. Chemical mechanical polishing may then be performed relative to the copper layer. Similar to the copper interconnection, a plug, which may be used to interconnect multi-layered metal interconnections, may also be formed by filling a via hole with tungsten, etc.
When forming a copper interconnection or a tungsten plug, a barrier layer may be necessary to prevent a metal from diffusing into other layers, and may enhance a bonding property relative to an insulating layer.
An interlayer dielectric layer, however, may have a certain amount of moisture. The moisture contained in the interlayer dielectric layer may be exhausted when forming the barrier layer at a high temperature. This may cause the barrier layer to be irregularly formed.
In addition, if the barrier layer is irregularly formed, a diffusion of metal may occur when the metal layer is filled in the via hole at a high temperature. Thus, a material forming the plug, such as tungsten, may not be easily introduced into the via hole, but may block an inlet of the via hole (which is called “overhanging”). Also, tungsten may be stacked up only around the inlet of the via hole.
Moreover, if the barrier layer is weakly formed, aluminum of the barrier layer's lower part may be discharged. Diffusion of metal may occur if a metal layer is formed by tungsten, etc. Aluminum (Al) in the barrier layer may react with fluorine of WF6 gas, which may be source material forming the plug. This may form AlF3. In addition, if AlF3 is discharged out of the via hole, the phenomenon of blocking introduction of W into the via hole in the process of W deposition may occur.